1. Field of the Invention
The present invention relates to the isomerization of bromohalogenobenzenes.
2. Description of the Prior Art
The isomerization of bromohalogenobenzenes is generally known to this art. Thus, published French Patent Application No. 2,362,807 describes the preparation of 1-bromo-3,5-dichlorobenzene by isomerization of 1-bromo-2,4-dichlorobenzene at 80.degree.-180.degree. C. in the presence of an aluminum halide, such as anhydrous AlCl.sub.3. Such process exhibits several disadvantages, however, which render its industrial application precarious. In fact, concurrently formed are numerous isomers of the desired product, i.e., 2,3-dichlorobromobenzene, 2,5-dichlorobromobenzene, 3,4-dichlorobromobenzene and 2,6-dichlorobromobenzene, while the product of industrial interest is 3,5-dichlorobromobenzene, a known intermediate for the facile preparation of 3,5-dichloroaniline. Thirdly, it will also be appreciated that in the subject process various dismutation products (dichlorobenzenes and dichlorodibromobenzenes) too are prepared. Accordingly, upon completion of the subject reaction, highly complex reaction mixtures result which can be separated into the individual components thereof only upon carrying out lengthy and costly separation processes. A last disadvantage that should also be mentioned is that elevated temperatures must be maintained in order to complete the reaction successfully.
Compare also Moyer & Bunnett, J.A.C.S. p. 1891, June 20, 1963, which describes the preparation of 1-bromo-3,5-dichlorobenzene from 1-bromo-2,4-dichlorobenzene in the presence of potassium anilide in liquid ammonia. The yields obtained by this process are very low (33%) and, in practice, preclude any industrial application thereof.
Therefore, serious need exists in this art for a process for the isomerization of bromohalogenobenzenes which enables the selective production of desired product under conditions of mild temperatures and also the ready recovery of final product while at the same time avoiding the use of solvents, the industrial handling of which is precarious and dangerous.